An information processing system is known to be constituted of at least one central processing unit or central host, formed of at least one central processor and one main memory to which the processor is connected; a plurality of peripherals; and at least one input/output processor assuring control of the exchange of data between the main memory and the various peripherals.
Peripheral control units, or controllers, are associated with various peripherals and assure the physical transfer of the data between the central host and the peripherals associated with the various controllers.
Generally, all the constituent functional elements of an information processing system at the same geographical location are connected to the same parallel bus, which assures the transportation of the data between the various boards that these elements have and the electrical power supply to the system.
A bus that is especially widely used at present is the Multibus II. Multibus II is a trademark of the Intel Corporation. The architecture of Multibus II is structured about a main bus of the parallel type, standardized by the Institute of Electrical and Electronic Engineers (IEEE) Standard 1296.
Mass memories, such as rotary magnetic disk memories or optical disk memories, are among the most-often used peripherals. They are very widely used, because they make the storage of very great quantities of information and relatively rapid access to the information possible. Their mean access time is on the order of 20 to 25 ms. The capacities of the highest-powered disk memories on the market exceed one gigabyte.
Among mass memories, memories known as electronic memories, also known as electronic disks (or solid-state disks), which use semiconductor memories, are currently being developed. Their access time is far less than a millisecond (that is, several tens of times less than the access time of the highest-powered rotary disk memories), and they have no rotating parts. Nevertheless, their unit memory capacity cost is still high, on the order of 20 times that for magnetic disk memories. However, the unit memory capacity cost of the electronic memories is decreasing much faster than that of rotary magnetic disk memories, and it can be expected that the cost will be equivalent within a few years. It may then be believed useful to use both rotary magnetic disk memories and solid-state disks as peripherals for an information processing system.
The structure of information processing systems is increasingly complex and requires more and more elements. Moreover, the volume of data to be processed by such a system is quite high and requires the use of an increasingly large number of mass memories where the data must be stored before being processed by the central processors of the system. As a result, the management of an entire such system by its central processing unit is extremely complex.
It is accordingly desirable to decentralize the management of the set of elements comprising an information processing system at the level of a plurality of subsystems, each of which manages one portion of the elements of the system, and in particular the peripherals.